<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*id选择器*/
        #div1 {
          color: green;
        }
    </style>
</head>
<body>
<div id="div1">id 选择器</div>
</body>
</html>